Investigating the dissociation energies of niobium and vanadium oxide clusters synthesized by ion sputtering

The mass distributions and fragmentation routes of Nb _n O _m ⁺ and V _n N _m ⁺ clusters sputtered from an metal surfaces with Xe⁺ ions under O₂ pressure of P = 4?5 × 10^?3 Pa in a bombardment chamber are studied by means of secondary ion mass spectrometry. The spectra of kinetic energy release distribution (KERD) are measured for the most probable routes of the fragmentation of Nb _n O _m ⁺ and V _n N _m ⁺ and clusters, on the basis of which the activation energies of the decomposition (dissociation) of Nb _n O _m ⁺ and V _n N _m ⁺ clusters are determined within the model of evaporative ensemble and the theory of monomolecular reactions. The results show the closeness of the numerical values of dissociation energies derived using both models.     

Fragmentation processes of vanadium and niobium oxide clusters sputtered by ion bombardment

The mass distribution of emitted V _n O _m ^? and Nb _n O _m ^? clusters and their unimolecular decay by all stoichiometrically possible fragmentation channels, which takes place under the sputtering of niobium and vanadium surfaces and blowing by oxygen, are studied. It is shown that the formation, excitation, and unimolecular fragmentation of V _n O _m ^? and Nb _n O _m ^? clusters can be described by a statistical recombination mechanism. Clusters are formed over the target surfaces as a result of binary collisions of independently sputtered ions, atoms, and molecules.     

Mechanism for the formation of molecular clusters under ion sputtering

The mechanism for the formation of molecular Si _n O _2n+1 ^? clusters above the surface during the recombination of ions, atoms, and molecules independently sputtered in individual cascades is presented. Clusters form when sputtering products Si, O, SiO and SiO₂ (monomers) join the active anion O^? successively as a result of pair collisions between them. The joining of monomers involves different combinations of them; in this case, the (Si _n O_2n+1)^? group is formed and consists of monomers with the same masses, but with different monomer compositions in the chain (combinatorial synthesis).     

Kinetic-energy release distributions and stability of niobium-carbon clusters sputtered from the surface of niobium carbide by xenon ions

The results of studying the emission and fragmentation of niobium-carbon clusters Nb _m C _n ⁺ synthesized upon sputtering a niobium carbide surface with Xe⁺ ions are presented. The fragmentation channels of Nb _m C _n ⁺ clusters are studied. We present the values of the dissociation energy of some Nb _m C _n ⁺ clusters (m = 1–7, n = 2–8) calculated within the context of the “evaporation ensemble” model and theory of unimolecular reactions based on performed measurements of the kinetic-energy spectra of fragment ions. The obtained results are compared with published data.     

Cluster projectile ions used for the SIMS analysis of silicon

Comparative studies of the emission of Si _n ⁺ (n = 1–11) cluster ions and impurity-containing polyatomic ions under bombardment of B-doped single crystal silicon with A _m ^? (m = 1–5) cluster ions with an energy of E ₀ = 6–18 keV are carried out. The peculiarities of sputtering an adsorbed-particle layer with cluster ions are revealed. The possibility of determining the depth distribution of adsorbed particles by analyzing the yield of sputtered heteroatomic molecular ions upon bombardment is demonstrated.     

Decay rate constants of sputtered vanadium oxide clusters

Results from studying the emission and fragmentation of V _n O _m ^± clusters sputtered from a vanadium surface by Xe⁺ ions at O₂ pressures of P = 4–5 × 10^?3 Pa are presented. The average decay rate constants of V _n O _m ^± clusters for major fragmentation channels are determined. It is shown that the decay rate constants for clusters of similar stoichiometry do not depend on their charge states.     

Toward the theory of electron and positron states in dielectric clusters

Analytical expressions for the binding energy of electrons and positrons in dielectric clusters, analyzed in this work, neglect the elastic effects. Therefore, we present the density-functional theory for neutral liquid clusters that experience the spontaneous deformation. Using the 1/R-expansion, R being the cluster radius, the exact analytical expressions for the size corrections to the chemical potential, surface tension, and atomic density are derived from the condition of mechanical equilibrium. The problem of calculating these corrections is reduced to calculating the quantities for a liquid with a flat surface. The size compression and tension of density occur in the 1/R and 1/R ² orders respectively. The sizes of charged rigid and elastic critical clusters, for which the electron or positron binding energy is close to zero, are calculated for Xe _N ^? , Kr _N ^? , Ar _N ^? , Ne _N ⁺ , He _N ⁺ . The calculations show significant contribution of self-compression to the binding energy of the excess electron in contrast to the positron.     

SIMS of silicon bombarded with Sb m + cluster ions

The emission of Si _n ⁺ (n = 1–11) cluster ions and Si _n X _m ⁺ (X stands for B or Sb) polyatomic ions when bombarding a single silicon crystal with Sb _m ⁺ (m = 1–4) cluster ions with energies E ₀ = 3–12 keV is studied. Considerable nonadditive enhancement of the yield of Si _n ⁺ cluster ions and most polyatomic ions is observed when the number of atoms in the bombarding cluster ions is increased. The sensitivity enhancement factor for detecting boron impurities is as high as 50 when the cluster-SIMS-molecule technique is applied.     

Study of the formation and unimolecular fragmentation of Si<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>O<Stack><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript><Superscript>+</Superscript></Stack> clusters under ion bombardment

The dependences of the emission and fragmentation of clusters sputtered by Xe⁺ ions from the surface of Si _n O _m ⁺ on the oxygen pressure near the bombarded surface are studied using secondary ion mass spectrometry. It is shown that the process of Si _n O _m ⁺ cluster formation under ion bombardment can be described within the framework of the mechanism of combinatorial synthesis by taking into account the mutual reversibility of the reactions of formation and unimolecular decay.     

Experimental g factor of hydrogenlike silicon-28

Using the first principles calculations, the mixed Au _n Zn _m ⁺ (n + m ?? 6) cluster cations and their monocarbonyls Au _n Zn _m CO⁺ have been investigated at the PW91 level. For the small Au _n Zn _m ⁺ , most ground-state isomers are planar structures. A significant odd-even oscillation of the highest occupied-lowest unoccupied molecular orbital energy gaps with the number of Au atoms is observed. Upon CO adsorption, the top site and C head-on adsorptions are most favorable in energy. Moreover, the optimized geometries indicate that the CO molecule prefers binding to Au atom of the Au _n Zn _m ⁺ clusters, which can be understood by the frontier molecular orbital theory in detail. From the theoretical calculations, the CO charge population, CO binding energy (BE) and the Gibbs free-energy change ??G generally decrease with the increase of the Zn content. It is found that the BE is highly related to the electron transfer between CO and the cluster cations. Furthermore, a linear correlation between ??G and the CO BE is found. The red shift in the CO stretching frequency is sensitive to the cluster size and composition. Our calculation suggests that CO reactive collision on Au₃Zn⁺ and Au₂Zn ₂ ⁺ may lead to the dissociation of the clusters with a Zn atom loss.     

Phosphorus clusters: Synthesis in the gas-phase and possible cagelike and chain structures

Experimental results on the gas-phase formation of neutral and cationic phosphorus clusters are presented. The clusters were synthesized by visible (532 nm) or UV (193 nm) laser ablation of crystalline red phosphorus under high vacuum conditions and were analyzed using TOF mass spectrometry. Neutral P_n clusters produced by 532-nm ablation are found to be even-numbered while P _n ⁺ cations are mainly odd-numbered, with P ₇ ⁺ and P ₂₁ ⁺ being the most abundant ions. For UV laser ablation, stable compound clusters, neutral P₇H₃ and P₂₃H₅, and cations P₂₃H ₆ ⁺ were synthesized for the first time. The formation of P_n clusters by thermal vaporization of red phosphorus into a cold He gas was also investigated and only small clusters (n<6) were found. Possible structures of the observed phosphorus clusters, as well as their formation mechanisms under different conditions, are discussed.     

Field detachment of the negatively charged water dimer

Beams of Ar _m (H₂O) ₂ ^? ,m=0 to 4, are passed through an electric field and separated with a quadrupole mass spectrometer. Form<=2 the signal disappears at 31±1 kV/cm. Form=3 and 4 and larger (H₂O) _n ^? (n≧6) no field detachment is observed up to 40 kV/cm. The application of these results to the binding of excess electron in water clusters is discussed.     

The predissociation of the 2σ u −1 (c 4Σ u − , v states of the oxygen molecular ion

The dynamics of predissociation of the 2σ _u ^?1 (c ⁴Σ _u ^? ), v vibrational states of the O ₂ ⁺ ion was studied theoretically using the method of coupled differential equations. The main equations describing the vibrational motions of nuclei in the adiabatic and diabatic approximations are given. The applicability scope of approximate methods for solving these equations was studied. The predissociation widths for the v = 0 and 1 vibrational levels were found to be Γ₀ = 0.054 meV and Γ₁ = 9.71 meV. This substantiated the results of recent observations of neutral fragments formed after the dissociation of the O₂ molecule. About 99% of the O ₂ ⁺ ions in the 2σ _u ^?1 (c ⁴Σ _u ^? ), v states were found to decompose to the O(¹ D) + O⁺(⁴ S) dissociation products.     

Low energy π-π resonances in the Veneziano model

We attempt to impose elastic unitarity on the forward π-π scattering using the Veneziano Amplitude together with a crossing symmetric subtraction term as an input. TheN/D method is used and thep, ? mesons are interpreted as CDD poles. The self consistency requirement led to the evalutation of the low energy parameters and theS andP-wave phase shifts. The values of the scattering lengths obtained area ₀ ⁰ =0.084m _π ^?1 ,a ₂ ⁰ =?0.024m _π ^?1 ,a ₁ ¹ =0.047m _π ^?3 .     

Comparative study of the semiempirical three-parameter potential energy functions for diatomic molecules

A comparative study is made of four three-parameter semiempirical potential energy functions for 32 electronic states of diatomic molecules and their ions:n ₂:X¹gS _g ⁺ ,B ³π_g,A ³ gS_u,C ³ _u,B′ ³ gS_u.a ¹ π_g, a′gS _u ^? ,Ω ¹δ_u N ₂ ⁺ :X ² gS _g ^gS +A ² π,C ² gS _u ⁺ ,B ² gS _u ⁺ CO:X¹gS⁺,a ³ π, a′³ gS_u,e ³ gS^?,d ³gD₁,A ¹π CO⁺:X²gS⁺,A ² π,B ²gS⁺ O₂:X³gS _g ^? ,B ³ gS_u,c ¹ gS _u ^? ,b ¹gS _g ^s ,a ¹ δ_g,c ³ δ_u O ₂ ⁺ :X ²π_g,A ² π_g, a¹ π_g,b ⁴ gS _g ^? A program for numerically integrating the radial Schrödinger equation by the Cooley method is worked out. Certain additional units are introduced to conserve computer time. The resulting vibrational levels are compared with the experimental levels for all the electronic states studied. It is concluded on the basis of this analysis that it is not possible to describe equally well all the electronic states of various molecules on the basis of any single three-parameter potential function. A method for choosing a potential function for describing some particular electronic state of a diatomic molecule is proposed.     

Correlation femtoscopy of Kaons in the SELEX experiment

Preliminary results from the correlation femtoscopy of identical kaons in the SELEX experiment (Fermilab E781) are presented. Kaons are selected in inclusive reactions of Σ^?C(Cu) interactions at an initial energy of 610 GeV. Kaon pairs are studied in all possible charged states: K _s ⁰ K _s ⁰ , K _s ⁰ K⁺, K _s ⁰ K^?, K⁺K⁺, K⁺K^? and K^?K^?. The source sizes of the hadronization region of neutral and charged kaon pairs are measured.     

Hölder’s inequality for matrices

We prove that for arbitraryn×n matricesA ₁,A ₂,…,A _m and for positive real numbersp ₁,p ₂,…,p _m withp ₁ ^?1 +p ₂ ^?1 +…+p _m ^/?1 =1, the inequality 1 $$|Tr(A_1 A_2 ...A_m )^2 |< \mathop {II}\limits_{k = 1}^m [Tr(A_k^\dag A_k )^{p_k } ]P_k^{ - 1} $$ holds.     

E2 andE3 transition strengths in some rare-earth nuclei

Coulomb excitation byα-particles of vibrational-like states in even-mass rare-earth nuclei is used to determine the reduced transition probabilitiesB(E2; 0 _gs ⁺ →2 _γ ⁺ ),B(E2; 0 _gs ⁺ →2 _β ⁺ ),B(E2; 2 _gs ⁺ →0 _β ⁺ ) andB(E2; 0 _gs ⁺ →3 _oct ^? ) in¹⁵⁰Nd,^{152, 154}Sm,^{154, 158}Gd,¹⁶⁴Dy and¹⁶⁶Er. TheB(Eλ; 0 _gs ⁺ →I=λ)-values range from 2.4 to 6.5 single-particle units for transitions to the 2 _γ ⁺ -states, 0.8 single-particle units for the 2 _β ⁺ -states and from 14.1 to 21.7 single-particle units for the 3^?-states.     

Description of the properties of the low-lying energy states in 100Mo with IBM2

The properties of the low-lying energy states for the 100Mo isotope is investigated within the framework of the proton-neutron interacting model IBM2.By considering the relative energy of the d proton boson to be diferent from that of the neutron boson and taking into account the dipole interacting among like-boson LπLπand LνLν,the low-lying energy spectrum is reproduced well.Particularly,the relative position of the energies for 2+1,0+2,2+2 and 4+1states shifted correctly fit the experimental data.The electromagnetic properties,including the key observable B(E2)reduced transition branching ratios and the E2 reduced matrix elements of the experimental data,are well described.Our calculations show possible shape coexistence in the 100Mo nucleus.     

Beta-delayed gammas and QEC-values in the decays of150m,152mHo and149Dy

^{150m, 152m}Ho, and¹⁴⁹Dy were produced by fusion-evaporation reactions of⁴⁰Ar with targets of natural indium and¹¹⁴Cd. Theβ-decays of the isotopes were reinvestigated with emphasis on high-excitation daughter states. The decay energies for selectedβ-transitions were measured from electron-capture to positron-decay ratios. Corrections forγ-feeding from higher-lying states were taken into account. The following Q_EC-values were derived for^150mHo,^152mHo, and^149mDy of 6819 ( _?100 ⁺¹¹⁷ , 6263 ( _?80 ⁺⁸⁹ ), and 3914 ( _?52 ⁺⁷⁶ ) keV, respectively.